Bonfires in Northern Ireland traditionally mark the night before the Twelfth. However, should the Twelfth fall on a Sunday, as it did in 2009, the public holiday is given in lieu on the preceding Monday. This means that some bonfires may also be held on a Sunday night.

Eleventh Night bonfires have involved sectarian and loyalistparamilitary displays. Symbols of Irish nationalism/republicanism (such as the Irish tricolour), and symbols of Catholicism, are often burnt on the bonfires.[1][6] The tricolours on such bonfires are often daubbed with sectarian slogans such as "Kill All Taigs" (KAT) or "Kill All Irish" (KAI).[7][8]Effigies, and posters of Irish nationalist election candidates, are also sometimes burnt, which has been condemned as "inciting hatred".[9] More recently, symbols of various immigrant communities, especially the large Polish immigrant community, have been burnt on the fires. The Polish Association of Northern Ireland, and others, have described this as "racist intimidation".[10]

Eleventh Night bonfires have raised health and safety concerns, as well as environmental ones.[1][11]

Bonfires are often built to be as large as possible. Some have been built near houses and other buildings. Roads are often damaged and, according to the British Broadcasting Corporation, clean-up and repairs made to roads due to bonfire-related damage can "cost thousands of pounds", with some roads needing to be resurfaced.[1]

A major concern that has risen to greater prominence in recent years is the pollution they cause. In some bonfires, despite bans by bodies such as Belfast City Council, tyres are burnt. Tyres produce many toxic chemical compounds when burnt, and therefore pose a major health issue.[1]

There have been attempts to make the bonfires more family-friendly and environmentally-friendly. In Belfast, a Bonfire Initiative has been set up. When joining the initiative, the community groups who organize bonfires agree to a number of conditions. A "bonfire committee" must be formed; the gathering of material for burning may only begin on 1 June; only wood can be burnt; and paramilitary flags and emblems must not be displayed at the bonfire site. In 2010, groups who forbore from burning nationalist flags or symbols were awarded an extra £100 funding.[6]

In 2009, Belfast City Council began promoting "beacons" as an environmentally-friendly alternative. It is a pyramid-shaped metal cage filled with willow wood-chips, and set on a base of sand to protect the ground underneath. The willow trees re-grow within a year of being cut down, making the bonfires more environmentally sustainable. By agreeing to use the beacons, the communities qualify for up to £1,500 of funding from Belfast City Council to hold a street party – as long as they do not fly paramilitary flags or burn tyres. Some loyalist communities in Belfast have begun using the beacons. The Orange Order, whilst recognising the importance of bonfires to Protestant culture, have issued calls for the organisers of bonfires not to burn tyres.[12] However, many others oppose the beacon, claiming that it infringes upon their traditions.[1]

^Simpson, Mark (12 July 2004). "Damping down the flames". BBC News Online. BBC. Retrieved 2011-07-17. [...] went out with one of the crews on their busiest night of the year - Bonfire Night. It is the eleventh hour of the eleventh night [...]